Method for Reducing Mercaptans in Hydrocarbons

ABSTRACT

A method for reducing mercaptan concentration in a liquid hydrocarbon, comprising: contacting a mercaptan-rich liquid hydrocarbon having a first concentration of mercaptan sulfur with a composition comprising an oxidizing agent and water wherein the molar ratio of the oxidizing agent to mercaptan sulfur in the mercaptan-rich liquid hydrocarbon is from 3:1 to 10:1; and separating the water from the liquid hydrocarbon to yield a mercaptan-depleted liquid hydrocarbon having a second concentration of mercaptan sulfur, the second concentration being less than the first concentration; wherein a major amount of mercaptan compounds in the mercaptan-rich liquid hydrocarbon are converted to at least one sulfur oxoacid or salt thereof, having the formula: 
       [RSO x ] n Y 
     wherein R is a hydrocarbyl group; x is an integer from 1 to 3; n is 1 or 2; and Y is hydrogen, an alkaline metal, or alkaline earth metal.

TECHNICAL FIELD

The invention relates generally to methods for reducing mercaptanconcentration in liquid hydrocarbons.

BACKGROUND

Some hydrocarbons, such as crude oil and jet fuel, contain significantamounts of mercaptans which may have an impact on the value of thesehydrocarbon streams. As a result, such hydrocarbon streams are usuallysold at a discount in the market. Thus, reducing the mercaptan contentcould substantially improve both the marketability and the value of suchhydrocarbons.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to a method for reducing mercaptanconcentration in a liquid hydrocarbon, comprising: contacting amercaptan-rich liquid hydrocarbon having a first concentration ofmercaptan sulfur with a composition comprising an oxidizing agent andwater wherein the molar ratio of the oxidizing agent to mercaptan sulfurin the mercaptan-rich liquid hydrocarbon is from 3:1 to 10:1; andseparating the water from the liquid hydrocarbon to yield amercaptan-depleted liquid hydrocarbon having a second concentration ofmercaptan sulfur, the second concentration being less than the firstconcentration; wherein a major amount of mercaptan compounds in themercaptan-rich liquid hydrocarbon are converted to at least one sulfuroxoacid or salt thereof, having the formula:

[RSO_(x)]_(n)Y

wherein R is a hydrocarbyl group; x is an integer from 1 to 3; n is 1 or2; and Y is hydrogen, an alkaline metal, or alkaline earth metal.

DETAILED DESCRIPTION

The following terms will be used throughout the specification and willhave the following meanings unless otherwise indicated.

“Liquid hydrocarbon” refers to crude oil or jet fuel.

“Crude oil” refers to all types of mineral oils found in nature. Crudeoil includes oils obtained from wells, shale, rock and/or sand amongothers. The term “crude” or “crude blend” is used interchangeably andeach is intended to include both a single crude and blends of crudes.

“Jet fuel” refers to hydrocarbons having a boiling range between 280° F.and 572° F. (138° C. and 300° C.).

“Mercaptan” refers to compounds of the general formula R—SH wherein “R”means a hydrocarbyl group and “SH” means a mercapto group.

“Hydrocarbyl” refers to hydrocarbyl radicals containing 1 to 48 carbonatoms including branched or unbranched, cyclic or acyclic, saturated orunsaturated species, such as alkyl groups, alkenyl groups, or arylgroups.

“Mercaptan-rich liquid hydrocarbon” refers to a liquid hydrocarbonhaving a mercaptan sulfur content of at least 200 ppm.

The unit “ppm” means parts per million.

The invention effectively reduces the level of mercaptan sulfur in aliquid hydrocarbon. A mercaptan-rich liquid hydrocarbon having a firstconcentration of mercaptan sulfur is contacted with a compositioncomprising an oxidizing agent and water wherein the molar ratio of theoxidizing agent to mercaptan sulfur in the mercaptan-rich liquidhydrocarbon is from 3:1 to 10:1; and separating the water from theliquid hydrocarbon to yield a mercaptan-depleted liquid hydrocarbonhaving a second concentration of mercaptan sulfur, the secondconcentration being less than the first concentration; wherein a majoramount of mercaptan compounds in the mercaptan-rich liquid hydrocarbonare converted to at least one sulfur oxoacid or salt thereof, having theformula:

[RSO_(x)]_(n)Y

wherein R is a hydrocarbyl group; x is an integer from 1 to 3; n is 1 or2; and Y is hydrogen, an alkaline metal, or alkaline earth metal.

The Composition: The composition for oxidizing the mercaptans comprisesan oxidizing agent and water. Examples of suitable oxidizing agentinclude, but are not limited to, hydrogen peroxide, hypochlorite salts,organic peroxyacids, percarbonate salts, and persulfate salts andmixtures thereof. The oxidizing agent is chosen such that it is solublein water or in a water and low molecular weight alkanol mixture. Typicallow molecular weight alkanols include methanol and ethanol. In oneembodiment, the oxidizing agent is an alkali or alkaline earth metalhypochlorite salt. Examples of such salts include sodium hypochlorite,potassium hypochlorite, calcium hypochlorite, and magnesiumhypochlorite. In one embodiment, the oxidizing agent is sodiumhypochlorite. Aqueous sodium hypochlorite solutions are widely availablecommercially in varying concentration ranges (typically 1-15 wt. %).

The pH of the composition may be adjusted by adding a suitable base tothe composition. Generally, the base is selected from alkali metalhydroxides and alkaline earth metal hydroxides. In one embodiment, thepH of the composition is from 7 to 14; in a second embodiment, from 8 to12.

Method for Reducing Mercaptan Concentration in a Liquid Hydrocarbon: Theconcentration of mercaptan sulfur in a liquid hydrocarbon is dependenton the source. In one embodiment, the liquid hydrocarbon is a crude oil.In another embodiment, the liquid hydrocarbon is a jet fuel.

In one embodiment, the liquid hydrocarbon contains at least 200 ppmmercaptan sulfur; in a second embodiment, at least 300 ppm mercaptansulfur; in a third embodiment, at least 400 ppm mercaptan sulfur; in afourth embodiment, at least 500 ppm mercaptan sulfur; in a fifthembodiment, at least 600 ppm mercaptan sulfur; in a sixth embodiment, nomore than 3000 ppm mercaptan sulfur.

A mercaptan-rich liquid hydrocarbon having a first concentration ofmercaptan sulfur is contacted with a composition comprising an oxidizingagent and water wherein the molar ratio of the oxidizing agent tomercaptan sulfur in the mercaptan-rich liquid hydrocarbon is from 3:1 to10:1, by means known in the art, such that a major amount of mercaptancompounds in the mercaptan-rich liquid hydrocarbon are converted to atleast one sulfur oxoacid or salt thereof, having the formula:[RSO_(x)]_(n)Y wherein R is a hydrocarbyl group; x is an integer from 1to 3; n is 1 or 2; and Y is hydrogen, an alkaline metal, or alkalineearth metal. The term “major amount” is understood to mean greater than50 percent by weight of mercaptan compounds in the mercaptan-rich liquidhydrocarbon. The composition can be introduced continuously orintermittently into operating gas or fluid pipelines. Alternatively,batch introduction can be used particularly for offline pipelines. Thecontact can be from 20° C. to 300° C.; in a second embodiment, from 20°C. to 100° C.: in a third embodiment, at room temperature. The amount ofthe composition to the mercaptan-rich liquid hydrocarbon is from 5:95 to95:5 volumetric.

In one embodiment, at least 60 percent by weight of the mercaptancompounds in the mercaptan-rich liquid hydrocarbon are converted to theat least one sulfur oxoacid or salt thereof; in a another embodiment, atleast 70 percent by weight of the mercaptan compounds in themercaptan-rich liquid hydrocarbon are converted to the at least onesulfur oxoacid or salt thereof; in yet another embodiment, at least 80percent by weight of the mercaptan compounds in the mercaptan-richliquid hydrocarbon are converted to the at least one sulfur oxoacid orsalt thereof.

The contact is for a sufficient time such that a major amount ofmercaptan compounds in the mercaptan-rich liquid hydrocarbon areconverted to at least one sulfur oxoacid or salt thereof having theformula: [RSO_(x)]_(n)Y, wherein R is a hydrocarbyl group; x is aninteger from 1 to 3; n is 1 or 2; and Y is hydrogen, an alkaline metal,or an alkaline earth metal. In one embodiment, the contact time is atleast 30 seconds; in a second embodiment, at least one minute; in athird embodiment, at least five minutes; in a fourth embodiment, atleast one hour; in a fifth embodiment, at least two hours; in a sixthembodiment, less than 24 hours.

Vigorous mixing is desired to minimize the formation of disulfides.Conventional methods in the prior art for removing mercaptans fromhydrocarbons typically involve “sweetening” wherein mercaptans areoxidized to form disulfides. Light mercaptans (C₁-C₄) may be removed inan aqueous wash in this process but removal of heavy mercaptans (C₄₊) isless effective due to the poor water solubility of heavy mercaptans.Disulfides which are derived from heavy mercaptans may decompose back tomercaptans at high temperatures, for example, during the distillationprocess. In the present invention, a major amount of mercaptan compoundsin the mercaptan-rich liquid hydrocarbon are converted to at least onesulfur oxoacid or salt thereof which are highly water soluble andtherefore easily removed from the hydrocarbon stream.

The water can be separated from the liquid hydrocarbon in a phaseseparation device known in the art, resulting in a mercaptan-depletedliquid hydrocarbon having a second concentration of mercaptan sulfur,the second concentration being less than the first concentration.Suitable phase separation devices include, but are not limited to,cyclone devices, electrostatic coalescent devices, gravitationaloil-water separators, and centrifugal separators.

In one embodiment, the mercaptan-depleted liquid hydrocarbon containsless than 50 ppm mercaptan sulfur; in a second embodiment, less than 40ppm mercaptan sulfur; in a third embodiment, less than 30 ppm mercaptansulfur; in a fourth embodiment, less than 20 ppm mercaptan sulfur; in afifth embodiment, less than 10 ppm mercaptan sulfur; in a sixthembodiment, less than 5 ppm mercaptan sulfur; in a seventh embodiment,less than 1 ppm mercaptan sulfur.

Method for Reducing Halide Concentration: The use of halide-containingoxidizing agents, such as sodium hypochlorite, may produce a halidetreated product having an organic halide impurity content, typicallyfrom about 40 to 4000 ppm. The presence of organic halides in suchtreated products may be undesirable. In one embodiment of the method forreducing mercaptan concentration in a liquid hydrocarbon, wherein theoxidizing agent is a halide-containing oxidizing agent, themercaptan-depleted liquid hydrocarbon is further contacted with anaqueous caustic solution under conditions to reduce the halideconcentration in the mercaptan-depleted liquid hydrocarbon.

In one embodiment, the aqueous caustic solution is selected from alkaliand alkaline earth metal hydroxide solutions, and mixtures thereof.Examples include lithium hydroxide, sodium hydroxide, potassiumhydroxide, calcium hydroxide, and magnesium hydroxide solutions. Inanother embodiment, the aqueous caustic solution is a sodium hydroxidesolution. In yet another embodiment, the concentration of caustic rangesfrom 0.001 N to 10 N. In one embodiment for mercaptan removal orreduction, the molar ratio of caustic to halogen-containing oxidizingagent is in the range of 0.05:1 to 1:1.

The mercaptan-depleted liquid hydrocarbon is contacted with an aqueouscaustic solution by means known in the art. Methods may be conducted asbatch, semi-continuous or continuous processes, as described above. Inone embodiment, the contact is from 20° C. to 300° C.; in a secondembodiment, from 25° C. to 200° C.; in a third embodiment, from 30° C.to 150° C.; in a fourth embodiment, from 70° C. to 100° C. Contact maybe done with vigorous mixing. In one embodiment, the contact time is atleast one minute; in another embodiment, at least five minutes; in yetanother embodiment, at least one hour; in still yet another embodiment,at least two hours; in one embodiment, less than 24 hours.

In one embodiment, the amount of aqueous caustic solution to themercaptan-depleted liquid hydrocarbon is from 5:95 to 95:5 volumetricfrom which halide is removed.

In one embodiment, the aqueous caustic solution further comprises a lowmolecular weight alkanol as a co-solvent. The low molecular weightalkanol may have straight or branched chain alkyl groups containing 1 to4 carbon atoms. Examples of suitable alkanols include methanol, ethanol,n-propanol, isopropanol, n-butanol, isobutanol and tert-butanol andmixtures thereof. Typically, the low molecular weight alkanol isethanol. In one embodiment, the amount of lower alkanol is from 1-49percent by weight based on the total weight of the solution; in anotherembodiment, from 5-25 percent by weight based on the total weight of thesolution.

In one embodiment, the aqueous caustic solution further comprises aphase transfer catalyst. Examples of suitable phase transfer catalystsinclude, but are not limited to, quaternary ammonium salts, phosphoniumsalts and pyridinium salts. If used, the phase transfer catalyst may bepresent in an amount from 0.001 to 0.5 mole equivalents of causticagent. In one embodiment, the phase transfer catalyst is a quaternarysalt. In one embodiment, the phase transfer catalyst iscetyltrimethylammonium chloride.

In one embodiment, after caustic treatment, the mercaptan-depletedliquid hydrocarbon is recovered resulting in a mercaptan-depleted liquidhydrocarbon with a reduced halide concentration. Any means of separatingthe aqueous caustic solution from the mercaptan-depleted liquidhydrocarbon may be used. Examples include decantation, gravityseparation, settler based on gravity, extractor and others that areknown in the art.

EXAMPLES

The following examples are given to illustrate the present invention. Itshould be understood, however, that the invention is not to be limitedto the specific conditions or details described in these examples.

Examples 1-5

A high mercaptan sulfur crude blend (RSH=400 ppm) was treated with anaqueous sodium hypochlorite solution for several minutes with vigorousstirring. The layers were allowed to separate and the treated crude oilwas collected. The mercaptan sulfur concentration in the treated crudeoil was determined by UOP Method 163-67. The results are set forth inTable 1.

TABLE 1 NaClO Concen- Reaction Total RSH in NaClO/RSH trationTemperature Time treated crude mole ratio (wt. %) (° C.) (min) (ppm) Ex.1 3 2 23 2 <1 Ex. 2 6 2 23 2 <1 Ex. 3 6 1 23 5 <1 Ex. 4 6 1 70 5 <1 Ex.5 6 1 70 10 <1

As shown, the mercaptan sulfur content of crude oils can be effectivelyreduced using the disclosed method.

Examples 6-9

A light jet fuel (boiling point range=350-450° F.) having mercaptansulfur content of 644 ppm and a heavy jet fuel (boiling pointrange=450-550° F.) having a mercaptan sulfur content of 408 ppm wereeach treated with aqueous sodium hypochlorite solutions for 5 minutes atroom temperature with vigorous stirring. The layers were allowed toseparate and the treated jet fuel was collected. The mercaptan sulfurconcentration in the treated jet fuel was determined by UOP Method163-67. The results are set forth in Table 2.

TABLE 2 NaClO RSH Content Concentration NaClO/RSH After OxidationDescription (wt. %) mole ratio (ppm) Ex. 6 Light Jet Fuel 1 6 <1 Ex. 7Light Jet Fuel 5 6 <1 Ex. 8 Heavy Jet 1 6 <1 Fuel Ex. 9 Heavy Jet 5 6 <1Fuel

As shown, the mercaptan sulfur content of jet fuels can be effectivelyreduced using the disclosed method.

Aqueous Phase Analysis: The sulfur content in the treated oil and in theaqueous layer may be analyzed to determine the extent of conversion ofmercaptan sulfur to sulfur oxoacids or salts thereof in the aqueousphase.

Example 10

A high mercaptan sulfur crude blend (RSH=644 ppm) was treated with a 1%aqueous sodium hypochlorite solution for several minutes at roomtemperature with vigorous stirring. The layers were allowed to separateand were collected. The total sulfur concentrations of the feed and thetreated oil were determined by X-ray fluorescence. The total sulfurconcentration in the aqueous was determined by ICP. The results are setforth in Table 3 as an average of five runs.

TABLE 3 Total sulfur in feed  0.24 g Total mercaptan sulfur in feed0.026 g Total sulfur in treated oil 0.214 g Total sulfur in water phase0.0207 g  Total sulfur recovered  0.23 g Overall sulfur recovery rate97% Sulfur in water as % of mercaptan sulfur in feed 80%

As shown, the results demonstrate that the total sulfur in the waterrepresent an 80% reduction of mercaptan sulfur.

Examples 11-12

A high mercaptan sulfur crude blend (RSH=644 ppm) was treated with anaqueous sodium hypochlorite solution with vigorous stirring. The layerswere allowed to separate and the aqueous layer was collected. Phenol wasadded into the aqueous phase to reduce sodium hypochlorite left in watersolution. The aqueous layer was then evaporated at 80° C. under vacuum.The solids were collected and dried at room temperature under vacuum forthree days. The relative amounts of sulfur oxoacids, or salts thereof,in the aqueous layer were determined by X-ray photoelectron spectroscopy(XPS). The results are set forth in Table 4.

TABLE 4 [RSO₃]_(n)Y Content Reaction Time NaClO/RSH After Oxidation(min) mole ratio (wt. %) Ex. 11 0.5 3:1 >89 Ex. 12 5 6:1 >90

As shown, the results indicate that over 89 wt. % of the sulfur speciesin the aqueous phase are sulfur oxoacids having the formula [RSO₃]_(n)Y.

Reduction of Chloride Content by Caustic Treatment

Comparative Example A

A halide-containing liquid hydrocarbon was prepared by treating a highmercaptan sulfur crude oil blend with a 1% aqueous sodium hypochloritesolution (6:1 NaClO:RSH molar ratio) for 5 minutes at room temperaturewith vigorous stirring. The layers were allowed to separate. The crudeoil treated with the halide-containing oxidizing agent was collected andthen washed several times with water. The organic chloride content inthe washed oil was determined according to ASTM D4929.

Examples 13-16

A halide-containing liquid hydrocarbon was prepared by treating a highmercaptan sulfur crude oil blend with a 1% aqueous sodium hypochloritesolution (6:1 NaClO:RSH molar ratio) for 5 minutes at room temperaturewith vigorous stirring. The layers were allowed to separate. The crudeoil treated with the halide-containing oxidizing agent was collected andthen washed with an aqueous caustic solution. The organic chloridecontent in the washed oil was determined according to ASTM D4929.

The chloride reduction results are set forth in Table 5.

TABLE 5 Chloride Content Washing Conditions (ppm) Comp. Ex. A Water, 25°C., 5 min. 71 Ex. 13 1N NaOH, 25° C., 0.5 min. 22 Ex. 14 1N NaOH, 20°C., 5 min. 16 Ex. 15 1N NaOH/EtOH, 40° C., 30 min. 11 Ex. 16 1N NaOH,90° C., 60 min. <1

As shown, aqueous caustic solutions are effective in reducing thechloride content of a crude oil treated with the halide-containingoxidizing agent using the disclosed method.

For the purposes of this specification and appended claims, unlessotherwise indicated, all numbers expressing quantities, percentages orproportions, and other numerical values used in the specification andclaims, are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that can vary depending upon thedesired properties sought to be obtained by the present invention. It isnoted that, as used in this specification and the appended claims, thesingular forms “a,” “an,” and “the,” include plural references unlessexpressly and unequivocally limited to one referent. As used herein, theterm “include” and its grammatical variants are intended to benon-limiting, such that recitation of items in a list is not to theexclusion of other like items that can be substituted or added to thelisted items.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to make and use the invention. The patentable scope is defined bythe claims, and can include other examples that occur to those skilledin the art. Such other examples are intended to be within the scope ofthe claims if they have structural elements that do not differ from theliteral language of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims.

1. A method for reducing mercaptan concentration in a liquidhydrocarbon, comprising: (a) contacting a mercaptan-rich liquidhydrocarbon having a first concentration of mercaptan sulfur with acomposition comprising an oxidizing agent and water wherein the molarratio of the oxidizing agent to mercaptan sulfur in the mercaptan-richliquid hydrocarbon is from 3:1 to 10:1; and (b) separating the waterfrom the liquid hydrocarbon to yield a mercaptan-depleted liquidhydrocarbon having a second concentration of mercaptan sulfur, thesecond concentration being less than the first concentration; wherein amajor amount of mercaptan compounds in the mercaptan-rich liquidhydrocarbon are converted to at least one sulfur oxoacid or saltthereof, having the formula:[RSO_(x)]_(n)Y wherein R is a hydrocarbyl group; x is an integer from 1to 3; n is 1 or 2; and Y is hydrogen, an alkaline metal, or alkalineearth metal.
 2. The method of claim 1, wherein the liquid hydrocarbon isa crude oil.
 3. The method of claim 1, wherein the liquid hydrocarbon isa jet fuel.
 4. The method of claim 1, wherein the liquid hydrocarboncontains at least 200 ppm mercaptan sulfur.
 5. The method of claim 1,wherein the oxidizing agent is an alkali or alkaline earth metalhypochlorite salt.
 6. The method of claim 1, wherein at least 60 percentby weight of the mercaptan compounds in the mercaptan-rich liquidhydrocarbon are converted to the at least one sulfur oxoacid or saltthereof.
 7. The method of claim 1, wherein at least 70 percent by weightof the mercaptan compounds in the mercaptan-rich liquid hydrocarbon areconverted to the at least one sulfur oxoacid or salt thereof.
 8. Themethod of claim 1, wherein the mercaptan-depleted liquid hydrocarboncontains less than 50 ppm mercaptan sulfur.
 9. The method of claim 1,wherein the mercaptan-depleted liquid hydrocarbon contains less than 10ppm mercaptan sulfur.
 10. The method of claim 1, wherein themercaptan-depleted liquid hydrocarbon contains less than 1 ppm mercaptansulfur.
 11. The method of claim 1, wherein the oxidizing agent is ahalide-containing oxidizing agent and the mercaptan-depleted liquidhydrocarbon is further contacted with an aqueous caustic solution underconditions to reduce the halide concentration in the mercaptan-depletedliquid hydrocarbon.
 12. The method of claim 11, wherein the aqueouscaustic solution is selected from alkali and alkaline earth metalhydroxide solutions, and mixtures thereof.
 13. The method of claim 11,wherein the aqueous caustic solution further comprises a low molecularweight alkanol.
 14. The method of claim 11, wherein the aqueous causticsolution further comprises a phase transfer catalyst.